System and Method for Joint Resurface Repair

ABSTRACT

An implant comprising a first, second, and third segment wherein the second and third segments partially overlap the first segment and define a load bearing surface comprising an anterior-posterior (AP) curvature including at least two tangential curves of the portion of the articular surface of the femoral condyle, the tangential curves having different radii of curvature. A drill guide comprises a body portion including a first, second and third bushing spaced along the body portion to establish a first, second and third axes, respectively. Each axis may be substantially normal to the articular surface at three different points along a curvature of the articular surface comprising the two tangential curves. A measuring device comprises a housing defining a longitudinally passageway and an outrigger. A guide pin may be received in the longitudinal passageway and a measuring device determines how far the guide pin is in the passageway.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/027,121 (now U.S. Pat. No. 8,177,841), filed Feb. 6, 2008, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/888,382, filed Feb. 6, 2007. U.S. patent application Ser. No.12/027,121 (now U.S. Pat. No. 8,177,841), filed Feb. 6, 2008, is also acontinuation-in-part of U.S. patent application Ser. No. 11/359,891 (nowU.S. Pat. No. 7,713,305), filed Feb. 22, 2006, which itself is acontinuation-in-part of U.S. patent application Ser. No. 10/373,463 (nowU.S. Pat. No. 7,678,151), filed Feb. 24, 2003, which is acontinuation-in-part application of U.S. patent application Ser. No.10/162,533 (now U.S. Pat. No. 6,679,917), filed Jun. 4, 2002, which isitself a continuation-in-part application of U.S. patent applicationSer. No. 10/024,077 (now U.S. Pat. No. 6,610,067), filed Dec. 17, 2001,which is itself a continuation-in-part application of U.S. patentapplication Ser. No. 09/846,657 (now U.S. Pat. No. 6,520,964), filed May1, 2001, which claims the benefit of U.S. Provisional Patent ApplicationSer. No. 60/201,049, filed May 1, 2000, all of which are incorporatedherein by reference. The entire disclosures of all of theabove-identified applications/patents are incorporated herein byreference.

FIELD

This disclosure relates to devices and methods for the repair of defectsthat occur in articular cartilage on the surface of bones, particularlythe knee.

BACKGROUND

Articular cartilage, found at the ends of articulating bone in the body,is typically composed of hyaline cartilage, which has many uniqueproperties that allow it to function effectively as a smooth andlubricious load-bearing surface. When injured, however, hyalinecartilage cells are not typically replaced by new hyaline cartilagecells. Healing is dependent upon the occurrence of bleeding from theunderlying bone and formation of scar or reparative cartilage calledfibrocartilage. While similar, fibrocartilage does not possess the sameunique aspects of native hyaline cartilage and tends to be far lessdurable.

In some cases, it may be necessary or desirable to repair the damagedarticular cartilage using an implant. While implants may be successfullyused, the implant should have a shape substantially corresponding to thearticular cartilage proximate the area where the implant is to be placedin order to maximize the patient's comfort, minimize damage tosurrounding areas, and maximize the functional life of the implant.

BRIEF DESCRIPTION OF DRAWINGS

The advantages and features of the present disclosure will become betterunderstood with reference to the following detailed description andclaims taken in conjunction with the accompanying drawings, wherein likeelements are identified with like symbols, and in which:

FIG. 1 illustrates the anterior-posterior (AP) curvature 10 of a typicalfemoral condyle.

FIG. 2 illustrates an isometric side view of one embodiment of animplant.

FIG. 3 illustrates an isometric bottom view of the implant shown in FIG.2.

FIG. 4 illustrates a plan side view of one embodiment of a drill guide.

FIG. 5 illustrates a perspective view of one embodiment of a measuringdevice.

FIG. 6 illustrates a plan side view of one embodiment of a guide pin.

FIG. 7 is a close-up of the distal end of the guide pin shown in FIG. 6.

FIG. 8 is a close-up of one embodiment of a reamer.

DETAILED DESCRIPTION

FIG. 1 depicts the anterior-posterior (AP) curvature 10 of a typicalfemoral condyle. The curve 10 depicted in this figure may berepresentative of an average of AP curves from a plurality ofindividuals. Such curvature values may be readily found in publishedmedical literature, for example, as may be reported in “ClinicalBiomechanics 18,” 2003, N. Nuno and A. M. Ahmed, which is fullyincorporated herein by reference. As can be seen in this Figure, the APcurvature 10 of the articular surface may generally include a pluralityof tangential curves having different radii of curvature.

For example, as shown in this figure, curve 10 may include a first orposterior curve 12 extending generally along the posterior region P ofthe femoral condyle. Curve 10 may also include a second or distal curve14 extending generally along the distal region D of the femoralcondyle), and a third or anterior curve 16 extending generally along theanterior region A of the femoral condyle. The first and second curves12, 14 may be approximately tangential about tangent point 18 and thesecond and third curves 14, 16 may be approximately tangential abouttangent point 20. The tangent points 18, are only approximations, andthe exact location of the tangent points 18, 20 may vary.

For exemplary purposes, while the AP curvature 10 may vary amongstindividuals, the posterior curve 12 may have span approximately 126degrees, the distal curve 14 may span approximately 73 degrees, and theanterior curve 16 may span approximately 38 degrees. Again, it should benoted that the extent of these curvatures may vary widely amongstindividuals, and these specific ranges are provided for exemplarypurposes only.

One aspect of the present disclosure is directed towards an implant thatapproximates at least a portion of the AP curvature 10 depicted inFIG. 1. For example, for a defect that spans at least part of the distaland posterior regions of the AP curve 10, an implant provided by thepresent disclosure may be configured to accommodate the posteriorcurvature 12 and the distal curvature 14 of the femoral condyle.Advantageously, and as will be described more fully below, the implantof the present disclosure may have an AP curvature that is defined usinga minimal number of data points along the AP extent of the femoralcondyle. This feature may enable, for example, minimally invasivemeasurement procedures and implant site preparation, in accordance withprevious disclosures incorporated by reference herein.

FIGS. 2 and 3 depict an implant according to one aspect of the presentdisclosure. FIG. 2 depicts an isometric side view of an implant 40. Theimplant 40 may include a load bearing (distal) surface 42 and a bonecontacting surface 44. Surface 44 may include, for example, three ormore segments 44 a, 44 b, 44 c. In this embodiment, the implant 40 hasan extended length along the AP dimension. In other words, implant 40 isgenerally longer in the AP dimension than the medial lateral (ML)dimension. For purposes of this example, it is assumed that the implant40 is to be placed along a region that covers at least part of both theposterior curvature 12 and the distal curvature 14 of the femoralcondyle depicted in FIG. 1. However, it is equally contemplated hereinthat the implant 40 may be configured to define a curvature anywherealong the AP curve 10 depicted in FIG. 1.

As a general statement, the curvature of the load bearing or distalsurface 42 of the implant 40 may be defined by the depth from areference plane (RP) to the load bearing surface 42 of the implant 40 attwo or more different locations along the AP extent of the implant 40.In the example of FIG. 2, reference plane RP is generally tangent to theload bearing surface 42 at a point 80 that passes through the referenceaxis 46. Reference plane RP may also be parallel to a tangential planeextending through the point 80 (e.g., the reference plane RP may beparallel to and offset a distance X from the tangent plane passingthrough point 80). Point 80 may be defined as a point of origin fromwhich depth measurements may be defined. Reference axis 46 may passthrough at generally the midpoint of the implant 40, i.e., through themiddle of segment 44 b.

According to one embodiment, at least one depth 50 a and/or 50 b fromthe reference plane RP to the surface 42 may be defined at a firstdistance R1 from the reference axis 46. At least one additional depth 52a and/or 52 b from the reference plane RP to the surface 42 may bedefined at a second distance R2 from the reference axis 46. As shown inthis example, the first distance R1 is illustrated as a first circlecentered about the reference axis 46 in the reference plane RP. Also asshown in this example, the second distance R2 is illustrated as a secondcircle centered about the reference axis 46 in the reference plane RP,where R1<R2. Reference axis 46 may pass through at generally themidpoint of the implant 40, i.e., through the middle of segment 44 b

Two or more depths, namely, at least one depth 50 a and/or 50 b taken atdistance R1 and at least a second depth 52 a and/or 52 b taken atdistance R2 from the reference axis 46. For example, the depth 50 a maybe defined as a distance between the reference plane RP and the surface42 at a point between the reference axis 46 and the posterior (P) end ofthe implant 40, while depth 50 b may be defined as a distance betweenthe reference plane RP and the surface 42 at a point between thereference axis 46 and the anterior (A) end of the implant 40.Additionally, the depth 52 a may be defined as a distance between thereference plane RP and the surface 42 at a point near the posterior (P)end of the implant 40, while depth 52 b may be defined as a distancebetween the reference plane RP and the surface 42 near the anterior (A)end of the implant 40.

In one exemplary embodiment, depths 52 a and 52 b may be assumedapproximately equal. In this case, only one depth 52 a or 52 b may bedefined, and thus, the curvature of surface 42 of the implant 40 may beapproximated using depths 52 a or 52 b and at least one of 50 a and/or50 b. The foregoing assumes that the reference axis 46 is approximatelynormal to the articular surface. However, in alternative embodiments, ifthe reference axis is not assumed normal to the articular surface, thenboth depths 52 a and 52 b may be used to define the AP curvature of thesurface 42 of the implant 40.

Each segment 44 a and 44 c, by virtue of the AP curvature defined bydata points 50 a, 50 b, 52 a, and/or 52 b, may also have a referenceaxis 84 and 82, respectively. Reference axis 82 may be substantiallynormal to the articular surface and substantially normal to the outersurface 42 of segment 44 c and passing through approximately the middleof segment 44 c. Likewise, reference axis 84 may be substantially normalto the articular surface and substantially normal to the outer surface42 of segment 44 a and passing through approximately the middle ofsegment 44 a. Since data points 52 a and 52 b may be approximately equaland implant 40 may be symmetrical about reference axis 46, the anglebetween reference axis 82 and 46, denoted as α₁ in FIG. 2, and the anglebetween reference axis 84 and 46, denoted as β₁ in FIG. 2, may thereforebe approximately equal.

Thus, by defining the AP curvature of surface 42 of the implant 40 in amanner described above, the curvature of surface 42 may include two (ormore) tangential, but distinct, curves of the femoral condyle. It shouldbe noted that in most cases, the values of depth 50 a and 50 b may beinversely related. Thus, in a typical scenario, as the value of 50 aincreases, the value of 50 b may decrease, and vice-versa.

As mentioned above, the implant 40 may include three or more segments 44a, 44 b, 44 c, wherein each segment 44 a, 44 b, 44 c has a referenceaxis 82, 46, 84, respectively. The first and the third segments 44 a, 44c may partially overlap the second segment 44 b about opposing ends ofthe second segment 44 b. In other words, the second segment 44 b maypartially overlap with each of the adjacent segments 44 a and 44 c. Asshown, one or more of the segments 44 a, 44 b, 44 c may includegenerally circular cross-sectional shape which has been truncated alongthe AP extent of the implant 40. In addition, any of the segments 44 a,44 b, 44 c may be truncated along the ML extent of the implant 40 aswell.

The distal or bone facing surface 42 of the implant 40 may include oneor more mounting features or fixation elements 64 for securing theimplant 40 to the femoral condyle. For example, the mounting feature 64may be configured to engage with a screw or the like (not shown) asdescribed in U.S. application Ser. No. 10/373,463 filed Feb. 24, 2003,U.S. Pat. No. 6,679,917 issued Jan. 20, 2004, U.S. Pat. No. 6,610,067issued Aug. 26, 2003, U.S. Pat. No. 6,520,964 issued Feb. 18, 2003, andU.S. Provisional Application Ser. No. 60/201,049 filed May 1, 2000, allof which are fully incorporated herein by reference. As shown, themounting feature 64 may include an opening 68 (such as, but not limitedto, a tapered opening) configured to engage with a corresponding post(not shown) of a screw. The opening 68 may be formed in a protrusion orthe like extending generally outwardly from the bone facing surface 44.Other configurations for securing the implant 40 to the femoral condyleare also possible and contemplated herein.

As shown, the mounting feature 64 may be disposed in the second segment44 b. However, one or more mounting features 64 may be provided in thefirst, second, and/or third segments 44 a, 44 b, 44 c. Optionally, themounting feature 64 (for example, the opening 68) may be axially alignedwith at least one of the axes 46, 82, 84. As shown, opening 68 of themounting feature 64 may be axially aligned with the reference axis 46.

FIG. 3 depicts an isometric bottom view of the implant 40. The APcurvature of the implant 40 may be defined as described above. The MLcurvature of the implant 40 may be defined by at least two depths 54 aand 54 b taken at a distance from the reference axis 46. For example,depth 54 a may be defined as a distance between the reference plane RPand the surface 42 at a point near the medial (M) end of the implant 40,while depth 54 b may be defined as a distance between the referenceplane RP and the surface 42 near the lateral (L) end of the implant 40.Based on these depths, the ML curvature of the surface 42 may beapproximated as described in U.S. application Ser. No. 10/373,463 filedFeb. 24, 2003, U.S. Pat. No. 6,679,917 issued Jan. 20, 2004, U.S. Pat.No. 6,610,067 issued Aug. 26, 2003, U.S. Pat. No. 6,520,964 issued Feb.18, 2003, and U.S. Provisional Application Ser. No. 60/201,049 filed May1, 2000, all of which are fully incorporated herein by reference.

In one embodiment, the system of the present disclosure may include akit that includes a plurality of implants 40 having various APcurvatures and optionally various ML curvatures as described above. Theset of implants may be based on the most common values for the AP and MLcurvatures based on the most likely femoral condyle implantation sitesas well as most likely values for the various depths along the AP and MLcurvatures described above. For example, in such a set of implants, oneor more of the AP depth values 50 a, 50 b, 52 a, and/or 52 b may varyfrom one implant to the next implant, for example, in ½ mm increments.In this case, an implant may be selected that most closely matches themeasurements obtained from the patient's articular surface as describedbriefly below. Alternatively, a custom-built implant may be fabricatedusing these depth values.

Obtaining the depth measurements along the AP curvature and ML curvaturemay be obtained using the measuring tool/outrigger as described inapplication Ser. No. 10/373,463 filed Feb. 24, 2003, U.S. Pat. No.6,679,917 issued Jan. 20, 2004, U.S. Pat. No. 6,610,067 issued Aug. 26,2003, U.S. Pat. No. 6,520,964 issued Feb. 18, 2003, and U.S. ProvisionalApplication Ser. No. 60/201,049 filed May 1, 2000, all of which arefully incorporated herein by reference.

However, in the case of the AP depth measurements, rather than using asingle measuring tool, two measuring tools may be used. For example, afirst measuring tool/outrigger having a radius of R1 may be used toobtain depth values 50 a and/or 50 b and a second measuringtool/outrigger having a radius of R2 may be used to obtain the depthvalues 52 a and/or 52 b, wherein R2>R1. Of course, the methodologydescribed in the aforementioned U.S. patents may be utilized using asingle common reference axis (e.g., axis 46) to obtain all themeasurements described herein.

The implant 40 according to the present disclosure, may be secured tothe patient's articular surface as described in application Ser. No.10/373,463 filed Feb. 24, 2003, U.S. Pat. No. 6,679,917 issued Jan. 20,2004, U.S. Pat. No. 6,610,067 issued Aug. 26, 2003, U.S. Pat. No.6,520,964 issued Feb. 18, 2003, and U.S. Provisional Application Ser.No. 60/201,049 filed May 1, 2000 hereby incorporated by reference.

FIG. 4 depicts a drill guide 100 consistent with another aspect of thepresent disclosure. Drill guide 100 may be used to establish a pluralityof axes used to create a plurality of excision sites, for example,excision sites in the articular surface corresponding to segments 44 a,44 b and 44 c of the implant 40. The use of a multi-axes drill guide isdescribed in U.S. patent application Ser. No. 11/169,326 (US2006/0020343) filed Jun. 28, 2005 hereby incorporated by reference inits entirety. As will be explained below, the drill guide 100 may beused to establish a plurality of axes 46, 82, 84 with respect to thearticular surface. Axes 46, 82 and 84 may be related to one anotherwhich may be used to guide a cutting instrument when forming theexcision sites in the articular surface for the implant 40.

The drill guide 100 may be selected based on the data points obtainedfrom the articular surface (described above). As with the implant 40described above, the system of the present disclosure may include a kitthat includes a plurality of drill guides 100 that correspond(approximately) to the data points obtained so that the angles α₂ and β₂substantially correspond to the angles α₁ and β₂ of the implant 40. Tothat end, the curvature of the drill guides 100 included in such a kitwill vary from one to the next, in order to establish the proper workingaxes 82 and 84.

Consistent with one embodiment, the drill guide 100 may generallyinclude a body portion 90 having a generally arcuate shape in which atleast a portion of the interior surface 101 of the drill guide 100 maybe configured to be disposed on at least a portion of an articularsurface where the implant site is to be provided. The drill guide 100may also include a first, a second, and a third drill bushing 92, 94,and 96. The first drill bushing 92 may be configured to be disposed onthe interior surface 101 of the drill guide body 90 and may extendgenerally radially inwardly from the drill guide 100. According to oneembodiment, the first drill bushing 92 may optionally have an outerdiameter that substantially corresponds to a hole drilled into thearticular surface which may be used to index the drill guide 100 on thearticular surface as will be discussed below. The first drill bushing 92may also include an opening or boss 98 extending through the drill guide100 and the first drill bushing 92. A longitudinal axis of the opening98 in the first drill bushing 94 may substantially correspond to thereference axis 46. The first drill bushing 92 may optionally include aseparate component from the body portion 90 of the drill guide 100 andmay be configured to be removably coupled to the body portion 90 of thedrill guide 100.

The second and third drill bushings 94, 96 may be disposed on the outersurface 103 of the drill guide body 90 and may be a spaced distance fromthe first drill bushing 92. The spacing of the second and third drillbushings 94, 96 may be determined based on the size of the segments 44a, 44 b and 44 c relative to one another, which, in turn, correspond tothe excision sites in the articular surface. The measurements define theAP curve, which determines the drill guide 100 to select the angularrelationship of the three axes. According to one embodiment, the secondand third drill bushings 94, 96 may optionally extend generally radiallyoutwardly from the drill guide 100. The second and third drill bushings94, 96 may also each include an opening or boss extending through thedrill guide 100 and the second and third drill bushings 94, 96.Longitudinal axes of the openings 105 and 102 may substantiallycorrespond to the working axis 82, 84, respectively, similar to workingor reference axis 46. One or more of the second and third drill bushings94, 96 may optionally include a separate component from the body portion90 of the drill guide 100 and may be configured to be removably coupledto the body portion 90 of the drill guide 100.

As is taught in the aforementioned published patent application, thedrill guide 100 may be coordinated or indexed with the location elementinstalled in the articular surface so that the first drill bushing 92may be oriented coaxial with the reference axis 46 defined by thelocation element. For example, a guide rod may be fitted extending fromthe location element, and the guide rod may be received through theopening 98 in the first drill bushing 92 of the drill guide 100.According to such an embodiment, the guide rod and the location elementmay be provided having mating features, such as mating precision tapers.The guide rod may, therefore, be aligned along the reference axis 46.Alternatively, the drill guide 100 and the location element may includecooperating features allowing the drill guide 100 and location elementto be coordinated, e.g. aligned, positioned, etc., in a predeterminedmanner. The first drill bushing 92 may bear against, or otherwiseinteract with, the location element to position the drill guide 100 at apredetermined height relative to the articular surface, based on theheight of the location element relative to the articular surface.

According to a related alternative embodiment, the drill guide 100 maybe indexed or positioned on the articular surface without the use of alocation element. Consistent with one such embodiment, the referenceaxis 46 may be established, for example as described above, and a holemay be drilled into the articular surface generally along the referenceaxis 46. The first drill bushing 92 may be sized and shaped to be atleast partially received in the hole drilled into the articular surfaceabout the reference axis 46. The respective sizes of the hole and thefirst drill bushing 92 may be coordinated to achieve a predeterminedtolerance and control the amount of movement, or slop, of the drillguide 100 relative to the articular surface. In one embodiment, a snugfit may be achieved between the first drill bushing 92 and the hole,thereby restricting movement of the drill guide 100 relative to thearticular surface.

With the drill guide 100 located on the articular surface and indexedwith the reference axis 46, the working axes 82 and 84 may beestablished relative to the articular surface and the reference axis 46.The working axes 82, 84 may be established by drilling reference holesinto the articular surface guided by the second and third drill bushings94 and 96. A location element may be installed into each of thereference holes created in the articular surface using the second andthird drill bushings 94, 96 of the drill guide 100 as described inapplication Ser. No. 10/373,463 filed Feb. 24, 2003, U.S. Pat. No.6,679,917 issued Jan. 20, 2004, U.S. Pat. No. 6,610,067 issued Aug. 26,2003, U.S. Pat. No. 6,520,964 issued Feb. 18, 2003, and U.S. ProvisionalApplication Ser. No. 60/201,049 filed May 1, 2000.

Once the working axes 82 and 84 and the reference axis 46 have beenestablished, portions of the articular surface (and optionallyunderlying subchondral bone) may be excised to provide excision sitescorresponding to segments 44 a, 44 b and 44 c of the implant 40.According to one embodiment, the articular surface may be excised usinga drill, rotating cutter, or other instrument for excising a generallycircular region of the articular surface and/or subchondral bone asdescribed in application Ser. No. 10/373,463 filed Feb. 24, 2003, U.S.Pat. No. 6,679,917 issued Jan. 20, 2004, U.S. Pat. No. 6,610,067 issuedAug. 26, 2003, U.S. Pat. No. 6,520,964 issued Feb. 18, 2003, and U.S.Provisional Application Ser. No. 60/201,049 filed May 1, 2000. Dependingupon the diameter of the cutting path defined by the cutting blade orblades of the cutting instrument, at least a portion of the cutting pathdefined by the sweep of the cutting instrument may extend outside of thewidth of the condyle at the excision site.

FIG. 5 depicts a measuring device 120 consistent with another aspect ofthe present disclosure. Measuring device 120 may be used to obtain ormap a plurality of points on a patient's articular surface. Instead of aseparate screw element, however, the measuring device 120 of the presentembodiment may include an integrally formed tap (described below) thatmay be readily advanced and removed into and from the bone. Themeasuring device 120 may comprise a housing 122 defining alongitudinally disposed passageway 124 therein. The housing 122 maycomprise an outrigger 126 extending generally outwardly from the distalend 128 of the housing 122 a predefined radial distance Rr from thelongitudinal axis of the housing 122. The housing 122 may also include awindow or aperture 130 having a plurality of measurementmarkings/indicia (generally indicated by 132) for generating ameasurement as will be described below.

The measuring device 120 may also feature a guide pin 134, as shown inFIGS. 5-8, configured to be rotatably disposed within the longitudinallydisposed passageway 124 of the housing 112. A distal end 136 of theguide pin 134 (best seen in FIG. 7) may include a tap 138 for boringinto the articular surface. The tap 138 may include fluted regions 139and cutting edges 140 which allow the guide pin 134 to be self drillingand self tapping.

The distal end 136 of the guide pin 134 may be inserted into thearticular surface by rotating the guide pin 134. This may be preformedby hand, but may optionally include the use of a drill or the like. Asthe guide pin 134 is rotated, the tap 138 bores and threads a hole intothe articular surface to secure the guide pin 134 relative to thearticular surface. The depth which the guide pin 134 is inserted intothe articular surface may be determined by one or more visual indicialocated on the guide pin 134. For example, the guide pin 134 may featurean indentation or indicia (such as, but not limited to, a laser markingor the like) 142 extending generally radially inwardly a predetermineddistance proximate the distal end 136 of the guide pin 134. In practice,a surgeon may screw the guide pin 134 into the articular surface untilthe indentation 142 is substantially coplanar with the articularsurface.

Once the guide pin 134 is inserted into the articular surface proximatethe region to be measured, the housing 122 of the measuring device 120may be placed axially along the guide pin 134. The measuring device 120may be rotated about the guide pin 134 until the outrigger 126 isproximate the area to be measured. Measurements may be obtained bycontacting the outrigger 126 with the articular surface and readingwhich of the marking indicia 132 along the window 130 of the housing 122are aligned with a visual indicia on the guide pin 134 (such as theproximate end 144, markings and/or indentations on the guide pin 134).This process may be repeated until the desired number of measurementsare obtained.

Once the desired number of measurements are taken, the housing 122 ofthe measuring device 120 may be removed from the guide pin 134. Usingthe guide pin 134 extending from the articular surface, a reamer 150,shown in FIG. 8, may be axially aligned along the guide pin 134. Thereamer 150 may be used to excise a region of the articular surface andmay comprise a shaft 151 which may be coupled to a drill device (suchas, but not limited to, a hand or power operated drill). The reamer 150may be rotated about the guide pin 134 such that the cutting surfaces152 of the reamer excise a portion of the articular surface.

As mentioned above, the present disclosure is not intended to be limitedto a system or method which must satisfy one or more of any stated orimplied object or feature of the present disclosure and should not belimited to the preferred, exemplary, or primary embodiment(s) describedherein. The foregoing description of a preferred embodiment of thepresent disclosure has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit the presentdisclosure to the precise form disclosed. Obvious modifications orvariations are possible in light of the above teachings. The embodimentwas chosen and described to provide the best illustration of theprinciples of the present disclosure and its practical application tothereby enable one of ordinary skill in the art to utilize the presentdisclosure in various embodiments and with various modifications as issuited to the particular use contemplated. All such modifications andvariations are within the scope of the present disclosure.

1. An implant for replacing a portion of an articular surface of a bone comprising: at least a first and a second segments each comprising a truncated, generally arcuate perimeter corresponding to a first, and a second overlapping generally circular excision site formed in said articular surface, respectively, wherein said second segments partially overlap said first segment on a first end of said first segment, said first and said second segments comprise a bone contacting surface and a load bearing surface, said load bearing surface comprising curvature corresponding to a curvature of said replaced portion of said articular surface of said bone.
 2. The implant of claim 1, wherein said bone contacting surface comprises a first mounting feature configured to secure said implant to said bone.
 3. The implant of claim 2, wherein said bone facing surface of said first segment includes said first mounting feature.
 4. The implant of claim 2, wherein said first mounting feature is configured to securely engage with a fastening element, said fastening element configured to be secured to said bone.
 5. The implant of claim 4, wherein said fastening element includes a mounting screw.
 6. The implant of claim 4, wherein said first mounting feature includes a tapered opening configured to engage with a tapered post of said fastening element.
 7. The implant of claim 4, wherein said first mounting feature includes a tapered post configured to engage with a tapered opening of said fastening element.
 8. The implant of claim 2, wherein said bone contacting surface further comprises a second mounting feature configured to secure said implant to said bone.
 9. The implant of claim 8, wherein said second mounting feature includes a protrusion extending generally outwardly from said bone facing surface.
 10. The implant of claim 2, wherein said bone facing surface of said first segment includes said first mounting feature and wherein said bone facing surface of said second segment includes said second mounting feature.
 11. The implant of claim 34, wherein said bone facing surface of said third segment includes a third mounting feature.
 12. The implant of claim 11, wherein said first, said second, and said third mounting features are axially aligned with said first, said second, and said third overlapping generally circular excision site formed in said articular surface, respectively.
 13. The implant of claim 1, wherein said load bearing surface comprises an anterior-posterior (AP) curvature and a medial lateral (ML) curvature
 14. The implant of claim 1, wherein said curvature of said load bearing surface comprises at least two tangential curves of said portion of said articular surface of said bone, said tangential curves having different radii of curvature.
 15. A method of forming an implant for replacing a portion of an articular surface, said method comprising: reaming a first portion of said articular surface to form a first generally circular excision site; reaming a second portion of said articular surface to form a second generally circular excision site partially overlapping said first generally circular excision site; and selecting an implant having first and second segments each comprising a truncated, generally arcuate perimeter corresponding to said first and second overlapping generally circular excision sites, respectively, wherein said second segment partially overlap said first segment on a first end of said first segment, said first and said second segments comprise a bone contacting surface and a load bearing surface, said load bearing surface comprising curvature corresponding to a curvature of said replaced portion of said articular surface of said bone.
 16. The method of claim 35, further comprising a placing a drill guide onto said articular surface and establishing a plurality of axes in said articular surface corresponding to said second and said third excision sites using said drill guide.
 17. The method of claim 16, wherein reaming said second and said third excision sites comprises advancing at least one reamer along said plurality of axes towards said articular surface, wherein said at least one reamer is rotated about said plurality of axes.
 18. The method of claim 15, further comprising securing said implant to bone beneath said articular surface.
 19. The method of claim 18, wherein securing said implant further comprises securing a fastening element into said bone and securing said implant to said fastening element.
 20. The method of claim 19, wherein said fastening element comprises a screw, and wherein securing said fastening element into said bone further comprises advancing said screw into said bone.
 21. The method of claim 19, wherein said implant and said fastening element are secured using a tapered frictional coupling.
 22. A drill guide for establishing a plurality of axes in an articular surface, said drill guide comprising: a body portion comprising a generally arcuate shaped interior surface, wherein at least a portion of said interior surface is configured to be disposed on at least a portion of said articular surface; and first and second bushings spaced along a length of said body portion and configured to establish first and second axes, respectively, wherein each of said first and said second axes are configured to be substantially normal to said articular surface at two different points, respectively, along a curvature of said articular surface comprising at least two tangential curves, said tangential curves having different radii of curvature.
 23. The drill guide of claim 36, wherein at least one of said first, said second and said third bushings are removably coupled to said body portion.
 24. The drill guide of claim 36, wherein said second bushing is disposed along said body portion between said first and said third bushings, and wherein a first angle α between said first axis and said second axis and a second angle β between said second axis and said third axis are substantially symmetrical.
 25. The drill guide of claim 22, wherein said second bushing extends generally outwardly from said interior surface of said body portion.
 26. The drill guide of claim 25, wherein said second bushing comprises an outer diameter substantially corresponding to a diameter of hole formed in said articular surface.
 27. The drill guide of claim 36, wherein said first and said third bushings extend generally outwardly from an exterior surface of said body portion.
 28. A device for measuring a portion of an articular surface of bone, said device comprising: a housing defining a longitudinal passageway extending from an open distal end, said housing further comprising an outrigger extending generally outwardly proximate said distal end a predetermined distance Rr from a longitudinal axis of said longitudinal passageway; a guide pin configured to be at least partially received in said longitudinal passageway of said housing; and a measuring device configured to determine how far said guide pin is received in said passageway.
 29. The device of claim 28, wherein said measuring device further comprises a guide window disposed on said housing, said guide window comprising a plurality of indicia representing said distance measurements.
 30. The device of claim 29, wherein said a proximal end of said guide pin is configured to align with at least one of said plurality of indicia to determine said distance measurements.
 31. The device of claim 28, wherein a distal end of said guide pin comprises threads configured to engage with said articular surface.
 32. The device of claim 31, wherein a distal end of said guide pin further comprises a tap including at least one fluted region and at least one cutting edge, wherein said guide pin is self-tapping.
 33. The device of claim 29, wherein said guide pin further comprises indicia disposed a predetermined distance from said distal-most end of said guide pin corresponding to an insertion depth of said guide pin into said articular surface.
 34. The implant of claim 1, further comprising a third segment comprising a truncated, generally arcuate perimeter corresponding to a third generally circular excision site formed in said articular surface, said third generally circular excision site overlapping with said second generally circular excision site, wherein said third-segment partially overlaps said first segment on a second end of said first segment, said third-segment comprising a portion of said bone contacting surface and said load bearing surface.
 35. The method claim 15, further comprising reaming a third portion of said articular surface to form a third generally circular excision site partially overlapping said first generally circular excision site on a second end of said first segment; and wherein said selecting further comprises selecting an implant having first, second, and second third segments each comprising a truncated, generally arcuate perimeter corresponding to said first, said second, and said second third overlapping generally circular excision sites, respectively.
 36. The drill guide of claim 22, further comprising a third bushing spaced along a length of said body portion and configured to establish a third axis substantially normal to said articular surface at a third point along a curvature of said articular surface. 